The Bad Astronomer writes: "50 years ago today, the US detonated a nuclear weapon 240 miles above the Pacific Ocean. Called Starfish Prime, it was supposed to help US scientists and the military understand how the Soviets might try to stop incoming nuclear missiles. What it actually did was blow out hundreds of streetlights in Hawaii 900 miles away, damage a half dozen satellites, and create artificial aurorae and intense radiation zones above the Earth. It taught the world what an electromagnetic pulse (EMP) was, and what the effects might be from a powerful solar flare, a nearby supernova, or a gamma-ray burst."